The present invention relates generally to a bicycle speed changer, and more particularly to a dual dial rod speed changing indicator.
The conventional dual dial rod speed changing indicator has a base board which is provided with two ratchet wheels, an advancing dial rod, a withdrawing dial rod, and a plurality of ratchet pawls. The two ratchet wheels are coaxially mounted such that they are coupled with the advancing dial rod and the withdrawing dial rod by the ratchet pawls. In operation, the advancing dial rod is pushed to turn so as to actuate the two ratchet wheels to turn a predetermined angle to engage the pawls, thereby completing the bicycle speed changing. Similarly, the withdrawing dial rod is pushed to actuate the ratchet wheels to turn in reverse a predetermined angle so as to return to a gear position. In light of the two ratchet wheels being superimposed, the entire structure is rather complicated. The component parts must be assembled with precision to ensure that the gear shifting is located with certainty.
The present invention is to provide a dual dial rod speed changing indicator which is simple in construction to ensure that the gear shifting is attained with certainty.
The present invention comprises a base board, a wire hub seat, an advancing member, and a withdrawing member. The wire hub seat is pivoted to the base board and is acted on by a first bias force. The wire hub seat has a first ratchet tooth portion and a second ratchet tooth portion. The advancing member has an advancing dial rod and an advancing ratchet pawl. The advancing dial rod is acted on by a second bias force and is pivoted to the base board to turn between a first position and a second position. The advancing ratchet pawl is acted on by a third bias force and is pivoted to the advancing dial rod. When the advancing dial rod is exerted on by an external force to swivel from the first position to the second position, the advancing ratchet pawl is acted on by the third bias force to mesh with a tooth of the first ratchet tooth portion, thereby actuating the wire hub seat to overcome the first bias force to turn. When the external force is removed, the advancing dial rod is acted on by the second bias force to swivel from the second position to the first position. The withdrawing member comprises a locating ratchet pawl and a withdrawing dial rod. The locating ratchet pawl is acted on by a fourth bias force and is pivoted to the base board to engage a tooth of the second ratchet tooth portion for locating the wire hub seat. The withdrawing dial rod has a push block and a locating tooth, and is acted on by a fifth bias force and pivoted to the base board to swivel between a third position and a fourth position. When the withdrawing dial rod is acted on by an external force to turn from the third position to the fourth position, the push block presses against the locating ratchet pawl which is forced to move away from the second ratchet tooth portion. The locating tooth is meshed with a tooth of the second ratchet tooth portion. When the external force is removed, the withdrawing dial rod is acted on by the fifth bias force to swivel from the fourth position to the third position. The wire hub seat is acted on by the first bias force to turn in reverse. The locating ratchet pawl is acted on by the fourth bias force to mesh with the next tooth of the second ratchet tooth portion to locate the wire hub seat.